Thermionic valve



July 2, 1940. 6, w. WARREN 2,206,491

THERMIONIC VALVE Filed Feb. 15. 1939 Inventor GEOFFREY W- WARRENPatented July 2, 1940 UNITED J srrA-rss THERE/[IONIC VALVE GeoffreyWilliam Warren, Eastcote, Pinner,

England, assignor to M-O Valve Company Limited, London, EnglandApplication February 15, 1939, Serial No. 256,482

' In Great Britain February 16, 1938 1 2 7 Claims.

This invention relates to thermionic values of the type comprisingwithin an evacuated envelope and along the same discharge path in theorder stated a cathode, a control grid, an auxiliary electrode, anaccelerating ezectrode and an anode, the gaps in the said auxiliary andaccelerating electrodes being similar and alined one with the other sothat'when the said auxiliary electrode is maintained at a potentialnegative (or possibly slightly positive) to the cathode, and theaccelerating electrode is positive to the oathode, the auxiliaryelectrode drives the electrons through the gaps in the acceleratingelectrode and prevents them from striking the accelerating electrode.The auxiliary and accelerating electrodes together form a screen betweenthe control grid and the anode.

The object of my invention is to produce valves of this type havingimproved operating characteristics and in particular to preventsecondary electrons from the anode returning to the acceleratingelectrode when the anode is negative to the accelerating electrode.

In some known valves secondary emission from the anode has beensuppressed by means of an additional electrode or electrodes maintainedat negative or zero potentials with respect to the cathode and situatedbetween the accelerating electrode and the anode either within oradjacent to the discharge path. The eflc'ect of such additionalelectrodes is to produce a potential minimum in the discharge pathbetween the accelerating electrode and the anode and my inventionconsists broadly in so designing the auxiliary electrode and arrangingthe accelerating electrode and anode relative to. it that a potentialminimum is obtained in the discharge path between the acceleratingelectrode and anode without the use of any such additional electrodes.

In order that this result should be obtained it is necesary that thepotential of the auxiliary electrode should influence substantially thefield in the space between the accelerating electrode and the anode;that is to say, the accelerating electrode must not shield the saidspace effectively from the auxiliary electrode. This condition may befulfilled by making the distance between the auxiliary and acceleratingelectrodes sufiiciently small compared with the distance be tween theaccelerating electrode and anode; or by providing the auxiliaryelectrode with a part extending beyond the accelerating electrode,either in the direction of the anode or in a direction perpendicular tothat in which the elecder 20 mm. in diameter.

trons mainly travel; or by combining these two features.

Valves made accordin'gto my'invention possess several advantages overthe usual forms of tetrode and pentode valve. valves of anode impedancegreater than one megohm may readily be obtained, while at the same timethe current to the accelerating electrode may be less than three percent and in some cases less than one per cent of the anode current.- Ithas; beenfound. that this latter feature results in a considerablereduction in the noise level compared with valves of the more usualtypes.

In order that my invention may be fully understood, I will now describefour embodiments of it by way of example making reference to the figuresof the accompanyingdrawing in which Figures 1 and 2 are respectively a.perspective view and a cross section of the electrodes of oneembodiment,

Figure 3 and Figure 4 are cross-sections of two other embodiments, and

Figure 5 is a longitudinal section of the fourth embodiment.

In all the figures, l is a thermionic cathode, 2 is a control electrode,3 is the auxiliary electrode and is connected to the cathode l, 4 is theaccelerating electrode and 5 is the anode.

' In Figure 1, the cathode .l is indirectly heated and has the form of anickel tube 26 mm. long and 1.2 mm. diameter coated with a thin layer ofalkaline earth oxides. The control electrode 2 is a helical grid of ovalcross section having an internal minor axis of 2 mm. and wound onsupport wires 1; the anode 5 is a hollow nickel cylin- The auxiliaryelectrode 3 is a hollow hexagonal prism made from nickel sheet 0.1 mm.thick and is pierced by apertures 8, 2 mm. in width, in the oppositefaces of the prism, which are parallel to the plane containing the gridsupport wires, the distance between these opposite faces being 3 mm.Additional screens, not shown, are placed at each end of the electrodesystem and connected electrically to the electrode 3, to reduce theelectrostatic capacity between the anode 5 and control grid 2. Theaccelerating electrode 4 consists of four straight wires, 0.3 mm. indiameter, the axes of which lie at the intersections of two parallelplanes, 2 mm. apart and perpendicular to the plane containing the gridsupport wires, with two parallel planes, 5 mm. apart and parallel to theplane containing the grid support wires; the

Thus, for example,

axes are symmetrically arranged with respect to the axis of the cathode.

In Figure 3 the auxiliary electrode is provided with fins 9 extendingtowards the anode. Otherwise the arrangement is the same as in Figuresciency is thereby obtained, particularly at very high frequencies, sincethe paths of the electrons through the control grid are straighter andthe transit time is reduced.

In the foregoing ernbodiments,'-"the influence of the potential of theauxiliary electrode on the field in the space between the, acceleratingelectrode and the anode is due largely to the extension of the auxiliaryelectrode beyond the accelcrating electrode. In Figure 5 the auxiliaryelectrode 3, and accelerating electrode 4, are in the form of twohelical grids the turns of which are alined; the distance between theseelectrodes is made so small that the aforesaid potential minimumexists'between the accelerating electrode and anode. For example thegrids 3 and 4 may be wound with wire 0.1 mm. diameter to a pitch of 1.5mm. and may be separated by a distance of less than 0.7 mm.

I claim:

1. A thermionic valve comprising within an evacuated envelope and alongthe same discharge path a cathode, a control grid, an auxiliaryelectrode, an accelerating electrode and an anode,

the gaps in the said auxiliary and accelerating ating electrode andanode.

2. A therminoic valve comprising within an evacuated envelope-a cathodein the form of a metal tube coated with electron emitting material, ahelical control grid surrounding the cath- "ode, an auxiliary electrodein the form of a hol-

